Drive train for logging-while-drilling tool

ABSTRACT

An improved drive train for coupling a motor to a signal generating, rotary type valve in a logging-while-drilling tool. The drive train includes a double planetary, speed reducing transmission, the input shaft of which is coupled to the motor by an automatically releasable clutch to prevent damage in the event the valve becomes jammed. The output shaft of the transmission is coupled to the rotor of the valve by means of a flexible coupling which reduces the reversing peak torque loads created by operation of the valve.

United States Patent [151 Hawk [4 1 Dec. 12, 1972 [54] DRIVE TRAIN FORLOGGING-WHILE- DRILLING TOOL [72] Inventor: Daniel E. Hawk, Duncanville,Tex.

[73] Assignee: Mobil Oil Corporation, New York Primary Examiner-Henry T.Klinksiek Attorney-William J. Scherback et a1. [22] Filed: June 16, 1971[211 Appl. No.: 153,653 [57] ABSTRACT 7 An improved drive train forcoupling a motor to a 52] us. Cl ..137/624.14, 259/DIG. 43, 33/307,Signal generating "nary tYPe valve in a lgging'while' 175/50 138/45251/81 drilling tool. The drive train includes a double planeta- 51 Int.Cl ..F16k3 1/44,G01v1/40 ry, Speed reducing transmission the input Shaftof [5 Field of s s/ o; 13 2 24 3 2414; which is coupled t0 the motor byan automatically 251/81;340/18LD,18 NC; 116/137 A, 139; 33/205, 307;138/45, 46; 175/40, 45, 46, 50;

releasable clutch to prevent damage in the event the valve becomesjammed. The output shaft of the transmission is coupled to the rotor ofthe valve by means 259/1,DIG. 43;73/151 t a of a flexible coupllng WhlChreduces the reversing References Cited peak torque loads created byoperation of the valve.

UNITED STATES PATENTS 7 Claims,6 Drawing Figures 8/1950 Goodard..137/624.14 X

PATENTED DEC 12 1972 SHEET 1 BF 4 FIG./

ATTORNEY PATENTEU EB 12 I972 3. 705.603

sum 2 UF 4 DANIEL E. HAWK INVENTOR ATTORNEY PATENTED 1973 3,705,603

' sum 3 0F 4 DAN E. H NVEN BY Edd? ami/8 A TTORNEY PATENTEDUEE 2 19733,705,603

SHEET u 0F 4 7 FIG. 5

DANIEL E. HAWK INVENTOR Nfiucls kufawzi/a ATTORNEY DRIVE TRAIN FORLOGGING-WHILE-DRILLING TOOL BACKGROUND OF THE INVENTION The presentinvention relates to a logging-whiledrilling tool and more particularlyrelates to an improved drive train in a logging-while-drilling toolwhich utilizes a motor actuated rotary valve positioned in the drillingfluid to generate a pressure wave signal representative of a loggedcondition.

The desirability of a system which is able to measure downhole drillingparameters and/or formation characteristics and transmit them to thesurface while the actual drilling of an earth well is being carried outhas long been recognized. Several such systems have been proposed andare commonly referred to as loggingwhile-drilling systems. Inlogging-while-drilling systems, one of the major problems exists infinding a means for telemetering the desired information from a downholelocation to the surface and having it arrive in a meaningful condition.

In this regard, it has been proposed to telemeter the desiredinformation by means of a pressure wave signal generated in andtransmitted through the circulating mud system normally associated withrotary drilling operations. The pressure wave signal which isrepresentative of a particular piece of desired information is generatedin the mud downhole near the drill bit by a generating tool and the wavetravels up the hole through the mud to a signal processor at thesurface. One logging-while-drilling system utilizing this technique oftelemetry is disclosed and fully described in U.S. Pat. No. 3,309,656 toJohn K. Godbey, issued Mar. 14,1967.

in a tool of the type disclosed in US. Pat. No. 3,309,656, a rotaryvalve is positioned in the circulating mud path near the drill bit. Amotor in the tool is energized in response to a measured piece ofdesired information to open and close said valve at a rate which willgenerate a pressure wave in the mud representative of the measuredinformation.

The motor is connected to the valve by means of a drive train whichincludes a speed reducing transmission. Since the overall length anddiameter of the logging-while-drilling tool is limited, thistransmission must be capable of substantially reducing the rotationalspeed of the motor while occupying a minimum volume and at the same timemust be rugged enough to withstand the heavy load demands made on thetransmission. Further, the transmission must be resistant to undue wearsince any play or backlash in the gears of the transmission canseriously affect the instantaneous rotational relationship between themotor and the valve which in turn affects the character of the generatedpressure wave.

The signal generating valve is similar to a power turbine in that it hasa stator and a rotor which rotate relative to each other. When the valveis in an open position, slots in the rotor and stator are aligned toallow flow therethrough. When the valve is in a closed position, theslots are misaligned to block flow. When the tool is in operation, thedrive train experiences loads other than those applied by the motor.These loads develop from the operation of the valve as it constantlyrotates'between its open and closed positions. This constantly reversingloading produces peak torques that must be compensated for in the drivetrain before they are applied to the transmission to prevent unduefatigue of the transmission. Also, these torques may cause prematurefailure of the shaft connecting the transmission to the rotor if theyare uncompensated for.

Another problem for the drive train results from large debris, e.g.,chunks of wood or the like, which may become entrained in the drillingmud. This debris is circulated down the drill string and can becomelodged in the slots through the rotor and stator of the valve, therebylocking the rotor against rotation. If this occurs and the motor in thetool continues to run, serious damage to the motor and drive train canresult. Therefore, the drive train should contain a means for preventingsuch damage in the event the valve becomes locked.

SUMMARY OF THE INVENTION The present invention provides an improveddrive train for'a logging-while-drilling tool of the type having amotor-actuated rotary valve to impart a pressure wave signal to thedrilling mud.

The improved drive train of the present invention connects the motor tothe rotary valve in the loggingwhile-drilling tool and includes acompact, heavy duty transmission for reducing the relatively high speedsof the motor to the much lower, operational speeds of the valve. Thedrive train also includes means to reduce the reversing peak torqueloads developed by the opening and closing of the valve and means toprevent damage to the motor and drive train in the event the valve jamsagainst rotation.

Structurally, the present drive train comprises a clutch meanspositioned between the output shaft of the drive motor and the inputshaft. of a speed reducing transmission. The clutch means provides apositive driving connection between the shafts under normal operatingconditions but automatically disengages to allow relative rotationalmovement between the shafts in the event that one of the shafts becomeslocked. The transmission is compact in both length and diameter but atthe same time is rugged and capable of handling the heavy loads appliedthereto. The transmission has a double planetary gear arrangement whichprovides the necessary speed reduction between the motor and the rotorof the valve.

The output shaft of the transmission is coupled to the shaft of therotor of the valve by means of a flexible coupling. The flexiblecoupling not only provides a positive driving connection between the twoshafts, but also has the proper compliance to reduce the high peaktorques produced by the reversing loads on the shafts which aredeveloped by the operation of the valve.

BRIEF DESCRIPTION OF THE DRAWINGS The actual construction, operation,and the apparent advantages of the invention will be better understoodby referring to the drawings in which like numerals identify like partsand in which:

FIG. 1 is a schematic elevation of a rotary drilling apparatus includingin vertical section a well containing a drill string in which thepresent invention is employed;

FIG. 2 is a schematic elevation, partly in section, of a portion of thedrill string of FIG. 1 having a loggingwhile-drilling tool mountedtherein which utilizes the present invention;

FIG. 3 is a detailed sectional view of the upper portion of FIG. 2;

FIG. 4 is a sectional view taken along section 4-4 of FIG. 3;

FIG. 5 is a detailed sectional view of the transmission of the presentinvention; and

FIG.6 is a sectional view taken along section line 6- 6 of FIG. 5.

DESCRIPTION OF THE PREFERRED I EMBODIMENT rotate string 24 and bit 27. Aswivel 33 is attached to the upper end of kelly 28 which in turn issupported by hook 32 from a traveling block (not shown). Thisarrangement not only supports the drill string 24 in an operableposition within'well 22 but also forms a rotary string 24, and exitsthrough openings (not shown) in drill bit 27 to pass outwardly into well22. The mud then circulates upward carrying drill cuttings with itthrough the annulus between the well and drill string 24 to the surfaceof the earth 23. At the surface, well head 41 is secured to casing whichis cemented in the well 22. Pipe 42 is connected to casing 39 forreturning the mud to pit 34.

As schematically illustrated in FIGS. 1 and 2, a logging-while-drillingtool 46 is located in drill collar 26 which forms a part of the lowerend of drill string 24 near bit 27 Tool 46 has a motor-actuated rotaryvalve which periodically interrupts the drilling fluid flowing throughthe valve to thereby generate a pressure wave in the fluid which isrepresentative of a measured downhole condition. This is the type oflogging-whiledrilling tool which is disclosed and described in US. Pat.No. 3,309,656. The present invention is directed to an improved drivetrain for coupling the motor to the valve. However, in order to fullyunderstand and appreciate the present invention, a brief description oftool 46 will be set forth.

A transducer means which is capable of measuring a desired downholecondition and converting the measurement to an electrical signal ispositioned downhole on or near tool 46. As illustrated, transducer means54, e.g., a strain gauge, is positioned on drill collar 26 to measurethe downhole weight on bit 27. The signal from transducer means 54 isapplied to electronic package 53 which is sealed in compartment 48 oftool housing 46a. For an example of such an electronic package, see US.Pat. No. 3,309,656. Circuitry in package 53, in response to the signalfrom means 54, allows a defined amount of power from electric powergenerator 50 in compartment 49 of housing 46a to flow to variable speed,electric motor 55 in compartment 47 of housing 46a. A turbine 52 drivenby the mud flow rotates generator 50 to produce electrical power. Motor55 in response to the amount of electricity passing through package 53,will drive rotor 56a of signal generating valve 56 through improveddrive train 57 at the rotational speed necessary to generate a pressurewave signal in the mud which is representative of the measuredcondition.

As shown schematically in FIG. 2 and more in detail in FIG. 3, drivetrain 57 comprises a speed reducing transmission 59, a clutch means 58which couples output shaft 55a of motor 55 with input shaft 59a oftransmission 59, and flexible coupling means 60 which couples outputshaft 59b of transmission 59 to rotor shaft 56b. Drive train 57 will nowbe described in detail for a better understanding of the presentinvention.

Looking to FIG. 3', motor 55 is mounted in upper compartment 47 of toolhousing 46a. Output shaft 55a of motor 55 is journaled by means ofbearings in housing 46a and is coupled to input shaft 59a oftransmission 59 by clutch means 58. Clutch means 58 may be of any typewhich provides a positive driving connection between the shafts undernormal operating conditions but allows the two shafts to move relativeto each other in the event that one shaft becomes locked againstrotation. Preferably the clutch is a nonfriction, positive-cog typeclutch which will release in either rotational direction when apredetermined torque is exceeded by either shaft relative to the other.Clutches of this type are commercially available, e.g., Torq-Tender soldby Helland Research and Engineering, Inc. of Navarre, Minnesota. Thepurpose of providing clutch 58 in drive train 57 will be set forth belowin the description of operation of the present invention.

Transmission 59, the details of which will be described below, providesthe desired gear reduction between motor 55 and rotor 56a. Output shaft59b of transmission 59 is journaled in housing 46a by means of bearing71. The shaft 59b is coupled to shaft 56b of rotor 56 by means offlexible coupling 60. This flexible coupling may be of any type whichcompensates for the reversing peak torque loads which are developed bythe operation of valve 56 and applied to the shafts. Preferably coupling60 is of the type which is commercially available under the trade nameUNI/FLEX, sold by the Lovejoy Flexible Coupling Company, Chicago,Illinois. This coupling as shown in FIG. 3 is comprised of two hubs 61joined together by means of individual layers of helically woundsprings. This construction allows instantaneous relative angulardisplacement between the shafts thereby providing the compliancenecessary to reduce the peak torque loads. The purpose of coupling 60will be discussed in more detail in the description below the operation.Rotor 56a is secured on shaft 56b by a tapered bushing 72 and nut 73.This provides a positive connection between the shaft and the rotor sono slippage will occur. A seal means 74 is used to seal the interior ofhousing 46a around shaft 56b. A stator 56c of valve 56 is fixed againstrotation on housing 46a.

Transmission 59 is a heavy-duty, two-stage planetary gear reducer whichcan handle large loads in a relatively small volume within housing 46a.As shown in FIG. 5, input shaft 59a is joumaled in transmission housing80 by means of ball bearings 81. Sun gear 82 is formed integral on shaft59a and cooperates with a plurality of planetary gears 83 which arerotatably mounted on first planet carrier 84. Integral with planetcarrier 84 is intermediate shaft 85 which in turn has second sun gear 86integral therewith. Sun gear 86 cooperates with a second plurality ofplanet gears 87 which are rotatably mounted on output planet carrier 88.Output planet carrier 88 is integral with output shaft 59b. Both sets ofplanetary gears ,83, 87, respectively, cooperate with ring gear 89, asis well known in the transmission art. It can be seen by using atransmission such as disclosed in FIG. 5 that the speed of motor 55 canbe greatly reduced in a very short overall length and still be ruggedand transmit the loads from the motor to the rotor. All gears intransmission 59 are of high quality gear steel, surface hardened, andmachined to precision tolerances to minimize backlash between the gears.

The operation of the invention is as follows. Loggingwhile-drilling'tool46 is positioned in drill collar 26 in drill string 24. Fluidcirculating down the drill string will pass through slots 90 (FIG. 3) inrotor 56:; and through slots 91 in stator 56c and on down through mudturbine 52 and out bit 27. As valve 56 continuously rotates between itsopen and closed positions, reverse loads occur on the valve. Thesereversing loads are applied through the shaft 56b to coupling member 60which, due to its compliance, reduces the peak torques thus produced.Without coupling 60, these torques would be applied directly totransmission 59 to cause undue fatigue of the gears in the transmission.As the gears wear, the instantaneous angular velocity relationshipbetween the motor 55 and rotor 56a degenerates and, accordingly,accurate signaling becomes difficult. The torque loads on shaft 56b,without coupling 60, also tend to fatigue the shaft itself andcontribute to early failure thereof.

Also, looking at FIG. 4, it can be seen that when slots 92 and 91 arealigned, a piece of wood or the like entering the slots could jam thevalve in an open position. If motor 55 were running through a directdrive into the valve 56, damage could occur to the motor. By use ofclutch 58, this possibility of damage to motor 55 is eliminated in that,if valve 56 jams, the torque will build up on the clutch, release same,and allow the motor to run freely without any damage to the motor, geartrain, etc.

What is claimed is:

1. A logging-while-drilling tool comprising:

a housing adapted to be positioned in a drill string of an earthdrilling apparatus wherein a drilling fluid which is circulated throughthe drill string will flow around said housing;

a rotary valve positioned on said housing so that at least a portion ofthe drilling fluid flowing through the drill string will flow throughsaid valve, said valve having a shaft joumaled in said housing;

a motor in said housing having a drive shaft and an operatingcharacteristic determined by a downhole condition measured by said tool;and a drive tram connecting said drive shaft of said motor to said shaftof said rotary valve, said drive train comprising:

a transmission having an input shaft and an output shaft;

first means connecting said drive shaft of said motor to said inputshaft of said transmission; and

second means connecting said output shaft of said transmission to saidshaft of said valve, said second means having means for reducing thereversing, opposed torque loads developed by operation of said rotaryvalve.

2. The logging-while-drilling tool of claim 1 wherein:

said second means comprises a flexible coupling.

3. The logging-while-drilling tool of claim 1 wherein said first meanscomprises:

a clutch means which is engaged under normal operating conditions toform. a positive driving connection between said drive shaft of saidmotor and said input shaft of said transmission but is automaticallydisengaged when rotation of one of said shafts is impaired to allowrelative rotation between said shafts.

4. The logging-while-drilling tool of claim 3 wherein:

said second means is a flexible coupling.

5. The logging-while-drilling tool of claim d wherein said flexiblecoupling comprises:

a first hub member affixed to said output shaft of said transmission;

a second hub member afiixed to said shaft of said rotary valve; and

helically wound spring means connecting said first and second hubmembers together.

6. The logging-while-drilling tool of claim 5 wherein:

said clutch means comprises a nonfriction, positivecog clutch.

7. The logging-while-drilling tool of claim 6 wherein said transmissioncomprises:

a transmission housing;

said input shaft journaled in said housing;

a first sun gear on said input shaft;

a first planet carrier having a first plurality of planetary gearsjoumaled thereon, said first planetary gears being driven by said firstsun gear;

an output shaft on said first planet carrier;

a second sun gear on said first planet carrier output shaft;

a second planet carrier having a second plurality of planetary gearsjoumaled thereon, said second planetary gears being driven by saidsecond sun gear;

said output shaft of said transmission on said second planet carrier;and

ring gear means in said transmission housing for mating with said firstand second planetary gears.

1. A logging-while-drilling tool comprising: a housing adapted to bepositioned in a drill string of an earth drilling apparatus wherein adrilling fluid which is circulated through the drill string will flowaround said housing; a rotary valve positioned on said housing so thatat least a portion of the drilling fluid flowing through the drillstring will flow through said valve, said valve having a shaft journaledin said housing; a motor in said housing having a drive shaft and anoperating characteristic determined by a downhole condition measured bysaid tool; and a drive train connecting said drive shaft of said motorto said shaft of said rotary valve, said drive train comprising: atransmission having an input shaft and an output shaft; first meansconnecting said drive shaft of said motor to said input shaft of saidtransmission; and second means connecting said output shaft of saidtransmission to said shaft of said valve, said second means having meansfor reducing the reversing, opposed torque loads developed by operationof said rotary valve.
 2. The logging-while-drilling tool of claim 1wherein: said second means comprises a flexible coupling.
 3. Thelogging-while-drilling tool of claim 1 wherein said first meanscomprises: a clutch means which is engaged under normal operatingconditions to form a positive driving connection between said driveshaft of said motor and said input shaft of said transmission but isautomatically disengaged when rotation of one of said shafts is impairedto allow relative rotation between said shafts.
 4. Thelogging-while-drilling tool of claim 3 wherein: said second means is aflexible coupling.
 5. The logging-while-drilling tool of claim 4 whereinsaid flexible coupling comprises: a first hub member affixed to saidoutput shaft of said transmission; a second hub member affixed to saidshaft of said rotary valve; and helically wound spring means connectingsaid first and second hub members together.
 6. Thelogging-while-drilling tool of claim 5 wherein: said clutch meanscomprises a nonfriction, positive-cog clutch.
 7. Thelogging-while-drilling tool of claim 6 wherein said transmissioncomprises: a transmission housing; said input shaft journaled in saidhousing; a first sun gear on said input shaft; a first planet carrierhaving a first plurality of planetary gears journaled thereon, saidfirst planetary gears being driven by said first sun gear; an outputshaft on said first planet carrier; a second sun gear on saId firstplanet carrier output shaft; a second planet carrier having a secondplurality of planetary gears journaled thereon, said second planetarygears being driven by said second sun gear; said output shaft of saidtransmission on said second planet carrier; and ring gear means in saidtransmission housing for mating with said first and second planetarygears.